Intensity Data Correction for the Distance Effect in Terrestrial Laser Scanners

Terrestrial laser scanning systems deliver geographic coordinates and backscattered intensity values, which are acknowledged as significant observations that can be used in a wide range of applications. However, the direct use of these original intensity data is not recommended because they are influenced by multiple variables, especially distance and incidence angle effects. Multiple studies have demonstrated the success of the Lambertian cosine law in correcting the incidence angle effect. The distance effect, which is inconsistent with the theoretical relationships of the laser range equation, is complex and differs significantly across various systems. In this study, the effect of distance on intensity data is investigated. A new correction method for different scanners is proposed. Using diffuse targets at different reflectance values, two sets of experiments are designed to estimate the parameters and validate the proposed method. Faro Focus^3D 120 and Faro Focus^3D X330 terrestrial scanners are utilized; results show that the ratio of the coefficient of variation of the corrected intensity to that of the original intensity of the said scanners is approximately 0.19 and 0.07, respectively. The proposed method is also applied to correct the distance effect of natural surfaces and to investigate its practicability. The results imply that the proposed method exhibits high accuracy and generality in removing the distance effect and can be used for actual mapping tasks and geological applications.